Typically, a semiconductor device requires a final metal (or metallization) layer. For this, a metal layer is for example deposited over the whole surface of the semiconductor device, e.g. an aluminum layer is deposited by means of a sputter process, is structured and passivated (e.g. by means of a stack including a plasma oxide layer and a nitride layer deposited by means of chemical vapor deposition). Alternatively, metal may be plated in a resist mask that is already structured (e.g. galvanic deposition of copper).
However, for final assembly of the semiconductor device open portions of the metal layer (i.e. open bonding pads) are typically required. Opening the passivation layer by means of etching using halogens typically leads to contamination of the opened pads which may corrode in the course of going from frontend processing to backend processing and during backend processing (e.g. sawing). This may lead to high fluctuations of bonding quality. In an extreme case, a pad may not be bondable (NSOP, non stick on pad problem). Further, the corroded pads may lower reliability of the finished semiconductor device.